The overall aim of this proposal is to correlate clinical phenotype with molecular genotype in congenital adrenal hyperplasia due to 21-hydroxylase deficiency. A large group of patients and their immediate family members will be studied for CYP21 mutations, and both prospective and retrospective analysis will be undertaken to determine how closely in vitro measures of 21-hydroxylase activity are related to the degree of enzyme dysfunction as predicted from in vitro expression studies of certain known mutations.